When beneficiating minerals by flotation, it is necessary that this mineral be preliminarily comminuted to the size of solids allowing to carry out the process of flotation. The optimum size of solid particles of the useful ingredient capable of floating up from the volume of the flotation pulp is different for each type of mineral, and depends largely on the density of the useful ingredient in such a mineral.
For example, with regards to an ore mineral beneficiated by widely known flotation machines the average size of solids normally ranges from 0.01 to 0.1 mm. For a diamond-containing mineral the optimum size of particles capable of floating up from the body of the flotation pulp is not more than 0.5 mm.
Reducing a mineral to the optimum particle size is accompanied by excessive comminution of the useful ingredient disseminated in the mineral to a size which is more than the upper limit of floatability, or to a size which is close to the optimum. As is known, reduction in the size of solid particles of the useful ingredient affects the value of such a useful ingredient. Such a loss of value is especially pronounced when over-comminuting a diamond-containing mineral.
It is also to be noted that the greater part of overall expenditures associated with beneficiating minerals falls on comminution, and is as large as 40% of all expenditures associated with mineral processing.
Therefore, it is especially important to increase the upper limit in the size of mineral particles subjected to processing in a flotation machine. The accompanying advantage is an increase in the efficiency of the equipment for comminuting minerals. For example, an increase in the upper limit of particle size from 0.2 to 0.3 mm results in a 30% growth in the efficiency of ball mills. In some instances larger grain-size concentrates are more amenable to subsequent processing. Large diamond crystals have a higher value than small ones.
With respect to a diamond-containing mineral, the upper size limit of the particles of a useful ingredient of the mineral capable of floating up from the body of a flotation pulp in the prior art floatation machines is not more than 1 mm.
Along with conventional floatation machines in which solid particles of a mineral float up from the body of the aerated pulp conveyed to a pulp circulation chamber, there are known froth floatation machines in which solid particles of a mineral are fed to the surface of the froth layer of the flotation pulp. As the froth layer can reliably hold solids of the useful ingredient of the mineral twice as large in size as solid particles of the useful ingredient capable of floating up from the body of the pulp, it seems more economically advantageous to use combination-type flotation machines.
There is known a flotation machine (cf., SU, A, 759,141) in which the froth concentrate has an upper size limit of solid particles of a diamond-containing mineral of 2 mm. This flotation machine includes a vertical cylindrical chamber for circulating the flotation pulp having a tapered bottom over which a funnel for feeding the flotation pulp is positioned. The top portion of the chamber has the form of a horn the base of which holds an annular comb. Gaps between the teeth of the comb serve to screen solid particles of fine fraction of the mineral capable of floating up from the body of the aerated pulp. Provided between the funnel for feeding the flotation pulp and top edge of the chamber is a Segner's wheel whose rotation causes the flotation pulp to move on the wheel blades and be thrown to the walls of the horn onto the surface of the annular comb. Solid mineral particles of coarse fraction of the useful ingredient are retained at the surface of the comb to be then carried to the surface of the froth layer, whereas solid particles of the fine fraction of the useful ingredient with the liquid phase of the flotation pulp are conveyed through the gaps of the comb to the interior of the chamber wherefrom the solid particles of the useful ingredient float up to the froth layer.
However, in this flotation machine solid mineral particles of coarse fraction spread non-uniformly on the surface of the comb due their higher concentration at points where the flotation pulp leaves the blades of the Segner's wheel. Therewith, some solid particles of the useful ingredient of coarse fraction are carried to the interior of the chamber resulting in irretrievable losses of the useful ingredient.
There is also known a flotation machine for beneficiating minerals (cf., SU, A, 1,183,180) capable of distributing solid mineral particles of coarse fraction across the froth layer of flotation pulp more uniformly. This flotation machine comprises a vertical cylindrical chamber for circulating the flotation pulp having a tapered bottom to which there are secured a pipe for feeding the flotation pulp carrying mineral particles of fine fraction and a pipe for discharging gange, an annular trough for collecting froth concentrate secured at the top of the chamber for circulating the flotation pulp, a group of tapered shells secured axially in the chamber for circulating the flotation pulp and spaced equidistantly in terms of the height of the chamber, the height and inclination angles of the generating lines of the tapered surfaces of the shells to their axes of rotation being substantially the same, the bases of larger diameter of the shells facing the top part of the chamber resting on one tapered surface outside the shells, the inclination angle of the generating line of this tapered surface to its axis of rotation being smaller than the inclination angle of the generating lines of the tapered surfaces of the shells, a group of pulp aerators secured at the walls of the pulp circulation chamber, and a means for feeding mineral particles of coarse fraction positioned over the chamber for circulating the flotation pulp.
In this flotation machine the means for feeding mineral solids of coarse fraction to the surface of the froth layer includes a rotatable plate having a tapered surface to serve as a guide of a flotation pulp carrying solid particles, the base of larger diameter of this tapered plate facing the froth layer. Provided inside the plate is a receiver with an annular slotted hole positioned over the peripheral edge of the plate wherethrough compressed air escapes.
This construction of the means for feeding mineral particles of coarse fraction ensures sufficiently uniform spread of the mineral particles of coarse fraction across the surface of the froth layer. However, along with solid particles of the mineral, the entire liquid phase of the flotation pulp containing a substantial quantity of oily froth suppressing reagents are conveyed to the pulp circulation chamber, which can lead to breaking of the froth layer whereby this layer partially loses its capacity to hold mineral solids of the useful ingredient. The total quantity of oily reagents is normally not less than by one order of magnitude greater than the quantity of such reagents necessary for wetting the solid particles of the useful ingredient present in the mineral.
In addition, this means for feeding mineral solids of coarse fraction is structurally overcomplicated. It is further to be noted that most of the oily reagent is evacuated from the chamber with the froth concentrate, this froth concentrate tending to accumulate in the recycling water in the course of a subsequent treatment thereof, and a quantity of the reagent is inevitably lost in dump waste products to pollute the environment.
It is therefore an object of the present invention to provide a flotation machine capable of ensuring a higher yield of large-size particles of the useful ingredient of the mineral being beneficiated.
One more object is to structurally simplify the means for feeding mineral solids of coarse fraction.